A common lens utilized in connection with gonioscopy, i.e., the viewing of the periphery of the anterior chamber of the eye, is known as the Swan-Jacob Gonioprism (the “Swan”) lens. The Swan lens comprises a contact lens having a posterior contact surface that conforms to the anterior surface of the cornea of an eye. The contact surface is generally spherical and has an optical axis that may be aligned with the optical axis of the eye. The contact lens also has an anterior surface that is offset in an anterior direction from the contact surface. More particularly, the anterior surface has an optical axis that intersects the optical axis of the contact surface. When the contact lens is positioned on the eye, the user may view the anterior chamber by looking into the anterior surface in a direction generally parallel to the optical axis of the anterior surface of the lens. The contact surface may be smaller than the cornea so that the lens can be moved around on the cornea to view various parts of the anterior chamber.
It is desirable to be able to view the periphery of the anterior chamber when the user's line of sight is along the optical axis of the eye. This is difficult or impossible to do with a Swan lens.